The attack on the entry checkpoint into Panjshir province killed five police officers and one intelligence officer assigned to the post, provincial police Chief Aziz Ghyrat said.

Seven civilian construction workers also were killed in the blast, which Gyrat said happened in the late afternoon as cars were lined up to be searched before entering the province on a narrow mountain road.

"When the police searched the car, they realized he was a suicide bomber and the attacker quickly detonated the explosives and blew up the car and himself," Ghyrat said.

Several other civilians in other vehicles were wounded in the blast, he said.

Many of the civilian victims were in a bus waiting to be searched, which marks the entrance into Panjshir from Parwan province, said Najim Khan, provincial deputy police chief of police.

Taliban spokesman Zabiullah Mujahid said in a text message to journalists that one of its fighters had exploded a car bomb in Panjshir.

The insurgency has intensified terror attacks across Afghanistan to sow insecurity and weaken the government as international forces prepare to withdraw by the end of this year.

Panjshir was known as a stronghold of resistance to the Taliban's hard-line Islamic rule over Afghanistan from 1996 to 2001, when the US-led invasion toppled their regime for sheltering al-Qaeda terrorist leaders in the wake of the September 11 attacks.

The province was the home of Ahmed Shah Massoud, the ethnic Tajik leader of the Northern Alliance who was dubbed "The Lion of Panjshir" for his defiance against the Soviets during the Afghan war in the 1980s and later in the anti-Taliban Northern Alliance.

Massoud was killed by two suspected al-Qaeda members posing as journalists two days before the September 11 attacks.

Presidential front-runner Abdullah Abdullah is also from Panjshir and once served as a close aide to Massoud. The Taliban hopes to disrupt security during the presidential elections, which look set for a runoff between former Foreign Minister Abdullah and ex-Finance Minister Ashraf Ghani in June.